In recent years, efforts are being made to realize small size and low cost video printers while pursuing printing of high picture quality and high definition images on special printing paper.
Referring now to drawings, an example of the above described conventional video printers is explained in the following. FIG. 3 is a side cross sectional view of a conventional video printing apparatus. In FIG. 3, the apparatus has a housing 14. A thermal head 1, a platen 2, and an ink sheet 3 constitute a recording unit. A pickup roller 8 which is rotatably arranged, a separating roller 7 which is also rotatably arranged, a reverse roller 16 which can be pressed to the separating roller 7 and can rotate in a reverse direction constitute a paper feed mechanism for sheet form printing paper 12. A printing paper cassette 311 stores the printing paper sheets 12 and can freely slide on a cassette guide 318 of the apparatus housing 14, and can be detached from the apparatus housing 14. The mechanism to transport printing paper sheets once they are fed comprises a lifting member 13 which presses the printing paper sheets to the pickup roller 8, a printing paper pressure plate 10 provided on the printing paper cassette 311 which pushes up the printing paper sheets 12 by means of the lifting member 13 while carrying the printing paper sheets 12, a switching guide 6 to switch over between paper feed and paper ejection, guiding members 15 to guide the printing paper sheets 12, a pinch roller 4 and a capstan roller 5 which drive the printing paper sheets 12 after they have been fed.
The paper ejection unit to eject the printing paper sheets 12 comprises a paper ejecting roller 20 and paper ejecting pinch roller 21. A conventional video printer additionally comprises an ejected-paper tray 309 to store the printing paper sheets 12 after they have been ejected, an ejected-paper tray cover 23 to keep dust off the ejected-paper tray 309, and a first paper detecting unit 17 and a second paper detecting unit 19 to detect the printing paper sheets 12, the first and second printing paper detecting units 17 and 19 consisting of, for instance, photosensors. A control unit 328 to control the video printer comprises electrical circuits and is located underneath the cassette guide 318.
Operation of the above described conventional video printer is explained in the following.
First, in FIG. 3, the printing paper cassette 311 storing a plurality of printing paper sheets 12 is loaded along the cassette guide 318 of the apparatus housing 14. When feeding the printing paper sheets, the lifting member 13 goes up and pushes up the printing paper pressure plate 10 thereby pressing the printing paper sheets 12 on the printing paper pressure plate 10 toward the pickup roller 8 and the first paper detecting unit 17 detects the existence of the printing paper sheets 12; if no printing paper sheet is detected the paper feed action is stopped and "No-Paper" indication is made on an indicator (not shown in the drawing) of the video printer. When a printing paper sheet is detected, the pickup roller 8 rotates and transports a plurality of the printing paper sheets 12.
Now, as the reverse roller 16 which has been detached from the separating roller 7 starts to rotate in the direction opposite to that of the paper feed while pressing the separating roller 7, thereby allowing only one sheet of the printing paper sheets 12 to be transported with the remaining sheets blocked. Guided by the guiding members 15 and the switching guide 6, the transported sheet of the printing papers 12 is forwarded to the second paper detecting unit 19, where the front end of the paper is detected, and the paper feed action is completed after the paper has passed the capstan roller 5 and the pinch roller 4. Subsequently, the printing paper sheet 12 is transported by the pressure and rotation of the capstan roller 5 and the pinch roller 4 and thermal transfer printing is made at the printing unit comprising the thermal head 1, the platen 2, and the ink sheet 3.
Upon detection of the trailing edge of the printing paper sheet 12 by the second paper detecting unit 19, the switching guide 6 turns downward to switch the transport route over toward the paper ejecting unit. After printing by the printing unit is completed, the printed paper sheet is driven by the paper ejecting roller 20 and the paper ejecting pinch roller 21, and ejected to the ejected-paper tray 309 and stored in lamination.
However, in the above described construction, in loading the printing paper cassette with a stack of printing paper sheets into the apparatus housing, high precision guiding members and a loading mechanism (not shown in the drawing) are required to load and securely fit it at a predetermined position, thereby resulting in an increased overall height of the apparatus. To prevent the possibility of improper loading, a printing paper cassette detecting switch (not shown in the drawing) to prevent any damage of the lifting member 13 or its linking mechanical components is also required. Additionally, a cassette locking mechanism (not shown in the drawing) is required to prevent the printing paper cassette from being removed during the printing operation. Thus, the conventional printer had problems of requiring a large number of components, complicated construction and an increased cost. It also required two printing paper detecting units 17 and 19 in between the printing paper cassette and the printing paper transport unit, again causing problems of increased number of components, complicated structure, and increased cost.